This invention relates to the use of wire bond connections among a set of electrical components mounted on a metal clad circuit board and, more particularly, to the inclusion of a system of cut-out regions in the metal cladding to reduce mutual coupling between adjacent wire connections for substantial elimination of crosstalk between parallel electric circuits.
Various forms of construction are employed in building electrical circuits. The form of construction varies in accordance with the types of components which are to be interconnected. By way of example, one common form of construction employs the interconnection of numerous circuit modules upon a circuit board which serves to support the circuit modules. Frequently, the circuit board is clad, at least on a top surface thereof facing the modules, with an electrically-conductive sheet, such as a metal sheet. Portions of the sheet my be cut away to form conductive strips which interconnect various terminals of the circuit modules. In the case of certain modules, manufacture of the circuit is facilitated by the use of relatively short wire segments which are spaced apart from the circuit board, and make direct connection among various terminals of the circuit modules.
A situation of particular interest employing the foregoing construction with the external wire segments is found in optical communications wherein solid-state lasers are employed as transmitting elements for generating short-duration light pulses which are radiated from individual ones of the lasers into corresponding optical fibers of a set of optical fibers constituting an optical transmission line. By way of example, a solid-state laser may be constructed in the form of a diode of gallium-aluminum-arsenide which generates a pulse of light upon excitation of the diode with a suitable pulse of current.
An electro-optical transmitter employing a set of laser diodes may be constructed by use of a circuit board which supports laser driver circuits and the laser diodes, the latter being excited by the driver circuits. The driver circuits are formed as individual modules. Also, each of the laser diodes is formed as an individual module including terminals for receipt of the electrical current, and also having a light-output port through which light is directed to an end of an optical fiber. Due to the physical shapes of the modules, it is the present manufacturing practice to connect some of the terminals of the modules by the metallic sheet or cladding on a circuit board, while other ones of the terminals are interconnected by segments of electrically-conductive wires.
In a typical arrangement of the electro-optical transmitter, the modules are arranged in a set of parallel channels wherein each channel has a driver module, the laser diode, and an optical fiber. The wire segments which interconnect the components of the respective channels are disposed parallel to each other in an array of wire segments.
A problem arises in that the wire segments are sufficiently close to each other to introduce a significant amount of mutual magnetic coupling of electric signals conducted by the wire segments in the respective signal channels. This results in crosstalk or coupling of signals between the channels. The reliability of the electro-optical communication is reduced because the crosstalk acts as a source of noise which may introduce error in the communication. It is noted that in the typical electro-optical communication system, pulse modulation of an optical carrier is employed. Pulse modulation rates as high as one GHz (gigahertz) are available at the present time. At such high pulse frequencies, wire segments having lengths of approximately one millimeter or less can have strong magnetic coupling for crosstalk between the wire segments.
By way of example in the construction of electric circuits with printed circuit boards, Yamazaki et al, U.S. Pat. No. 4,758,805 discloses in FIGS. 7 and 19 connections in the form of partial loops from pins to conductive strips on a circuit board. Similar construction is shown in FIGS. 2 and 8 of Saburi et al, U.S. Pat. No. 4,782,310.